Convergence circuit



May 7, 1968 c. M. HART CONVERGENCE CIRCUIT Filed Feb. 26, 1965 2Sheets-Sheet 1 R q. w M Q N A nl I m R P HORIZON DEFLEC GENER a a M.- lC a z E 45 .9 a 4 C a 5 b u. a 2 a L E :7 m c R r, a b 2% M R R 5 if? mE E 2 O R V N O N E H G L N ATOR RTICAL LECTI GENERAT VERTICAL ONCONVERGENCE OR GENERATOR DEF AMPLIFIER FUNCTION GE NERATOR INVERTERFUNCTION GENERATOR INVENTOR.

CLEVE M. HART ATTORNEY C. M. HART May 7, 1968 CONVERGENCE CIRCUIT 2Sheets-Sheet 2 Filed Feb. 26, 1965 INVENTOR C LEVE M. HART fifl AM/LATTORNEY United States Patent 3,382,400 CONVERGENCE CIRCUIT Cleve M.Hart, Ben Lomond, Calif., assignor to Sylvania Electric Products Inc., acorporation of Delaware Filed Feb. 26, 1965, Ser. No. 435,547 8 Claims.(Cl. 315-13) This invention relates to information display and moreparticularly to a circuit for controlling convergence of electron beamsin a multi-beam shadow mask color kinescope.

Present day air traffic control systems, radar systems and other typereconnaissance systems often provide a large amount of information in ashort time. The human operator of such systems is frequently required tosimultaneously observe a number of targets or analyze many signals. Ingeneral, he must process a large amount of information in a short time.One method of facilitating the processing of this information is toselectively display it in color. In an air traffic control system,aircraft assigned to a particular flight pattern may be indicated in onecolor on a color kinescope, aircraft being interrogated may be indicatedin another color and aircraft not yet in an area requiring interrogationmay be indicated in still another color.

In an electromagnetic reconnaissance direction-finding system,directional information may be represented by a polar display on akinescope. The position of the indication on the kinescope, with respectto a reference point and reference plane, indicates the direction of theelectromagnetic signal. The position of the indication wth respect tothe reference point is a function of the magnitude of the signal. Thefrequency spectrum monitored by the system may be divided into a numberof frequency bands and each frequency band indicated by a differentcolor on the kinescope. Thus, the operator can quickly determine thefrequency band and direction of received signals by the color of theindication on the kinescope. In the latter system, the electron beams ofthe color kinescope are moved about the face of the tube in a randommanner.

Most present day color television receivers employ a color kinescopewherein three electron beams are focused through apertures in a shadowmask onto a screen comprised of a plurality of separatephosphor dots.The dots are arranged in triads. Each triad consists of a red, a blueand a green phosphor dot. Each dot in each triad emits either red, greenor blue light when an electron beam is incident on it. In order toobtain a clear display, special circuitry is provided to insure that theelectron beams are incident on phosphor dots of a single triad. Adifferent convergence circuit and electromagnet is associated with eachcolor. Each convergence circuit develops a convergence signal that isapplied to the associated electromagnet. Convergence circuits associatedwith displays having periodic or raster type scans, such as intelevision receivers, are complex and contain frequency sensitivecircuits such as tuned circuits, the resonant frequency of which isrelated to the scan rate. Such circuits do not generate properconvergence signals in applications where the electron beams move aboutthe face of the tube in a random manner.

An object of this invention is the provision of convergence circuitryfor a color kinescope wherein the electron beams are moved about theface of the tube in a random manner.

Another object is the provision of convergence circuitry for a colorkinescope employing frequency insensitive circuits.

Another object is the provision of circuitry for color kinescopes forgenerating convergence signals that are in- 3,382,409 Patented May 7,1968 dependent of the rate the electron beams sweep across the face ofthe tube.

Another object is the provision of convergence circuitry that may bemade as an integrated circuit.

In accordance with this invention, a convergence signal is generated bya convergence circuit employing frequency insensitive circuits. Selectedportions of a deflection signal are attenuated. Selected portions of thedeflection and attenuated signals are inverted and again attenuated toproperly shape the input deflection signal. The gain of the output ofthe convergence circuit may be adjusted or the output applied directlyto the convergence electromagnet of the kinescope.

This invention and these and other if its objects will be more fullyunderstood from the following description of a preferred embodimentthereof, reference being had to the accompanying drawings in which:

FIGURE 1 is a perspective view of a color kinescope partially cut awaytogether with control circuitry embodying this invention;

FIGURE 2 is a fragmentary view of a phosphor screen illustratingconvergence of electron beams;

FIGURE 3 is a fragmentary view of a phosphor screen illustratingmisconvergence of electron beams:

FIGURE 4 is a block diagram of a convergence circuit embodying thisinvention;

FIGURE 5 is a circuit diagram of the embodiment of FIGURE 4; and

FIGURE 6 is a representation of an actual polar display formed by acolor display system employing this invention.

Referring now to the representation of FIGURE 1, the control circuitrycomprises convergence generators 21 and 22 that incorporate thisinvention. The shadow mask kinescope 1 comprises electron beam sources2, 3 and 4 energized by a signal processor 5. Electron beam sources 2, 3and 4 produce electron beams 6, 7 and 8 associated with blue, green andred primary colors, respectively. An apertured shadow mask 9 is disposednear a screen 10 of triads of phosphor dots at the end of kinescope 1opposite from the electron beam sources.

The arrangement of phosphor dots on screen 10 is illustrated in FIGURES2 and 3. The phosphor dots are arranged in the same order (red, greenand blue) in each row. Reference to the red phosphor dot 11 in FIGURE 2reveals that each phosphor dot is surrounded only by phosphor dots ofthe other two primary colors. Each triad is comprised of a red, a greenand a blue phosphor dot.

The point of incidence of the electron beams on screen 10 is controlledby signals produced by horizontal deflection generator 13 and verticaldeflection generator 14, which are also energized by signal processor 5.The deflection signals from generators 13 and 14 are applied on lines 15and 16, respectively, to the deflection yoke 17 of the shadow maskkinescope.

At any one time, the three electron beams 6, 7 and 8 preferably passthrough the same aperture of mask 9, each beam being incident on adifferent associated phosphor dot of the same triad as represented bythe shaded dots at 18 in FIGURES 1 and 2. When the electron beams aremisconverged they are incident on phosphor dots of different triads asrepresented by the shaded dots in FIGURE 3.

Convergence of the electron beams onto the phosphor dots of a singletriad is controlled by signals generated by horizontal convergencegenerator 21 and vertical convergence generator 22. The horizontal andvertical convergence generators operate on the output of the associateddeflection generator to provide convergence signals applied on lines23a, 23b and 230 and 24a, 24b

and 24-0 to convergence electromagnets 25a, 25b and 250, respectively.Each convergence electromagnet is associated with a particular primarycolor and has a horizontal deflection winding and a vertical deflectionwinding (not shown) connected to the output of the associatedconvergence generator. Each convergence generator comprises threephysically identical convergence circuits. Each convergence circuit isassociated with a different primary color and has an output connected tothe associated winding of the associated convergence electromagnet. Thisinvention is directed to the provision of the improved convergencecircuit illustrated in FTGUR'ES 4 and 5.

Referring now to the embodiment of this invention in IGURE 4, eachconvergence circuit comprises a function generator 2-6, an inverter 27,a function generator 23 and an amplifier 29. Function generator 26operates on the deflection signal generated by the associated deflectiongenerator to attenuate selected portions thereof. Portions of the outputof generator 26 are inverted by inverter 27. Function generator 28operates on the output of inverter 27 to attenuate selected portions ofthe modified deflection signal. The output of function generator 23 maybe amplified or applied directly to the associated winding of anassociated convergence electromagnet 25.

Referring now to the embodiment of this invention shown in FIGURE 5,function generator 26 comprises diode 31 and potentiometer 37. connectedbetween input line 36 and a reference potential. A second diode 31' andpotentiometer 32' are also connected between the input line and thereference potential. The anode of diode 31' and the cathode of diode 31are connected to the input line. The output of function generator 26 iscoupled through a Zener diode 33 to inverter 27 which comprisesdifference amplifier 34 and full wave rectifier 35. Zener diode 33 isconnected to the base of transistor 36 of the difference amplifier.Diode 33 provides a negative DC level shift at the input of theamplifier so the amplifier output can swing below the reference level.Rectifier comprises diodes 37 and 38 connected between the collectorelectrodes of transistors 36 and 36. The output of rectifier 35, andinverter 27, is coupled from the junction of diodes 37 and 38.

Function generator 28 comprises a resistor 41 connected between theoutput of rectifier 3S and a negative supply potential V Resistor 41 isshunted by a first voltage divider comprising resistors 42 and 43. Aplurality of diode circuits 44 are connected to the junction ofresistors 42 and 43. Each diode circuit comprises a diode 45 and asecond voltage divider comprised of resistors 46 and 47. Resistors 46and 47 are connected between the reference potential and a positivesupply potential +V The anode of diode 4-5 is connected to the junctionof resistors 46 and 47. The cathode of diode 4-5 is connected to thejunction of resistors 42 and 43. The magnitude of the output of functiongenerator 28 on line 48 is controlled by a variable attenuator 50. Itwill be noted that neither inverter 27 nor function generator 26 or 28contain frequency sensitive elements such as tuned circuits.

In order to facilitate understanding this invention, the operation of aconvergence circuit incorporating the invention is described in relationto obtaining the parabolic wave signals employed to converge theelectron beams in a color television receiver.

The deflection signal applied on line 30 to function generator 26 is thelinear ramp signal indicated at 51 in FXGURE 5. In a televisionreceiver, the negative and positive half cycles of the ramp signal maycorrespond to the right and left side or top and bottom of the kinescopescreen. During the negative half cycle between times t and t diode 31 isforward biased and conducts. Conduction of diode 31 reduces the slope ofthe ramp signal between times and t by shunting a portion of the signalto ground. Diode 31 is reverse biased and cut off during the positivehalf cycle of the ramp signal between times 1 and t Conversely, diode 31is forward biased and conducts during the positive half cycle of theramp signal between times t and t Diode 31' is reverse biased and cutoff during the negative half cycle of the ramp signal from time t to 1The slope of the output of function generator 26 between times t and tis varied by adjustment of potentiometer 32, whereas the slope betweentimes t and I is controlled by potentiometer 32'. In the particularexample described here, potentiometer 32' is adjusted to provide a veryhigh impedance so the slope of the ramp signal between times t and t isunchanged as indicated in the waveform at 52.

The output of function generator 26 (indicated at 52) is amplified bydifference amplifier 34. The outputs of the difference amplifier areindicated at 53 and 54. The output at 53 is 180 degrees out-of-phasewith the input at 52. Conversely, the output at 54 is in-phase with theinput at 52 and is 180 degrees out-of-phase with the output at 53.

The output 53 of amplifier 34 causes diode 37 to conduct between timest, and t to pass the positive halfcycle of the signal represented at 53.Diode 37 is cut off between times t and f Conversely, the output 54 ofamplifier 34- causes diode 38 to conduct between times and to pass thepositive half-cycle of the signal represented at 54. Diode 38 is cut offbetween times and 1 The output of rectifier 35 illustrated at 55 is thesame as the output of function generator 26 (waveform 52) except thatthe signal between times t; and I is inverted.

The resistances of resistors 46 and 47 the selected to provide apredetermined bias potential at the junction of the resistors to forwardbias the associated diode Each diode (45, is biased to conduct when theoutput of the rectifier is a different potential. For example, biaspotentials of +2.0 volts and +1.0 volt might be impresed on the anodesof diodes 45 and 45, respectively, by the associated resistors 46, 4'7and 46, 47', re spectively. In this example, diode 45 conducts andshunts a portion of the signal on line 48 to ground when the si nalpotential on the cathode is less than +2.0 volts. Similarly, diode 45'conducts when this potential is less than +1.0 volt and shunts more ofthe signal on line 43 to ground. Each diode continues to conduct untilthe oath ode potential is more positive than the signal potential atwhich the diode initially started to conduct.

The output of function generator 28 is illustrated at 56. It is largerthan the other waveforms in order to better illustrate the operation offunction generator 28.

The output of inverter 27 (waveform at time t; is more positive than thebias on the anodes of diodes 45 and 45 and the diodes are cut off. Attime t (see Waveform 55) the output of the inverter has decreased inmagnitude sufiiciently to cause diode 45 to conduct to shunt a portionof the inverted signal to ground. Diode 45, however, is still reversebiased and cut off. Conduction of diode 45 causes the slope of thesignal on line 48 to decrease at time 12;.

At time 21 (see waveform 56) the output of the inverter has decreased inmagnitude sufficiently to also cause diode 45 to conduct to shunt moreof the inverted signal to ground. Conduction of both diodes 45 and 45'causes a further decrease in the slope of the signal on line 48.

At time r (see waveform 56) the output of the inverter has increased inmagnitude sufficiently to reverse bias and cut off diode 45. This causesthe slope of the signal on line 48 to increase since the signal is nolonger shunted to ground through diode 45. Similarly, at time the outputof the inverter has increased in magnitude sufficiently to also reversebias and cut off diode 45. This causes a further increase in the slopeof the signal on line 48 since neither diode 45 nor 45' shunts thesignal on line 48 to ground. Thus, the signal on line 43 and the outputof inverter 27 have the same slope after time t The signal on line 48 isa very close approximation of a parabola. The fidelity of this signal online 48 may be improved by adding more diode circuits in shunt withdiode circuits 44 and 44'. The magnitude of the convergence signal online 48, waveform 56, is controlled by potentiometer 50. The convergencesignal on line 48 may also be amplified or applied directly to anassociated winding of an associated convergence electromagnet.

In most instances, the same convergence signal will not converge all theelectron beams. A slightly different signal is required to converge eachelectron beam. For a particular shadow-mask tube, for example, the rateof change of the slope of the convergence signal required for horizontalconvergence of the electron beam associated with the red phosphor dotson the left side of the screen varies more rapidly than the slope of theconvergence signal required for horizontal convergence of the electronbeam associated with the green phosphor dots on the left side of thescreen. Selective shaping to obtain the necessary convergence signal isachieved by selection of resistors 46 and 47 for biasing diodes 45, byadjustment of potentiometers 32 and 32', and by adjustment ofpotentiometer 50 or the gain of amplifier 29.

One method of adjusting the convergence circuits to converge theelectron beams of the color kinescope is as follows. Horizontaldeflection generator 13 is caused to generate a horizontal sweep on thekinescope. When the three electron beams are not properly converged,three lines (red, blue, green) occur which are not coincident.Potentiometers 32, 32' and 50 and the gain of amplifier 29 of eachhorizontal convergence circuit are adjusted to converge the three lines.Vertical deflection generator 14 is then caused to generate a verticalsweep on the kinescope. If the electron beams are not properlyconverged, three vertical lines occur which are not coincident.Potentiometers '32, 32 and 50 and the gain of amplifier 29 of eachvertical convergence circuit are adjusted to converge the three lines.After the convergence circuits are adjusted to converge linear signals,the horizontal and vertical deflection generators are caused to generatea circle or similar waveform having a symmetrical geometricconfiguration on the outer portions of each quadrant of the kinescope.Potentiometers 32, 32' and 50' and the gain of amplifier 29 of allconvergence circuits are again adjusted to converge the geometricconfigurations that occur when the electron beams are not properlyconverged. This process is repeated until the beams are satisfactorilyconverged.

By Way of example, convergence circuits similar to the one illustratedin FIGURE 5 were employed to converge the electron beams in a colordisplay system that provided the polar display shown in FIGURE 6.Components and values of elements employed in these convergence circuitsare:

R, 200o P (1) R, 4.3Ko P 1K9 R 3K9 P (1) R 3009 D 1N916 R 3K9 D (1) R3.3Ko D 1N73 R 1.5Kn D, 1N755 R 1.5K!) D 1N27O R, 33Ko D 1N270 R isKo D1N270 R ISOKQ D 1N270 R ZZKQ Q ZN697 R SZKQ Q 2N697 R14 +V1 V 15 4'3KQ-V 10V P 1K9 V V The signal on line 48 was applied to a variable gainamplifier rather than employing these components.

Although this invention is shown and described in relation to apreferred embodiment thereof, variations and modifications will beapparent to those skilled in the art. The scope and breadth of thisinvention is, therefore, to

be deter-mined from the following claims rather than from the abovedetailed description of a preferred embodiment thereof.

What is claimed is: 5 1. In a color display including a multi-beamlcinescope and means for providing deflection signals for deflecting thebeams, a convergence circuit for developing a signal for controllingconvergence of a beam, said convergence circuit comprising a firstfunction generator having an input and passing a deflection signal andhaving an output, said first function generator comprising first andsecond potentiometers having first terminals connected to a referencepotential and having second terminals,

a first diode having a first electrode connected to said input andhaving a second electrode connected to the second terminal of said firstpotentiometer,

a second diode having .a first electrode connected to the secondterminal of said second potentiometer and having a second electrodeconnected to said input,

said first and second diodes conducting to bypass a portion of thedefiection signal when the value of the deflection signal is less thanand exceeds a predetermined threshold value, res'pectively, and

an inverter comprising a difference amplifier responsive to the outputof said first function generator for generating a first output in phasewith the output of said first function generator and a second output 180degrees out-of phase with the output of said first function generator,and

a full-Wave rectifier responsive to the outputs of said differenceamplifier and passing said in-phase signal when it passes in onedirection a prescribed value and passing said out-of-phase signal whenit passes in the opposite direction said prescribed value, and

a second function generator having an input passing the output of saidrectifier and having an output, said second function generatorcomprising a first supply potential,

a first voltage divider having a first terminal connected to the outputof said rectifier and having a second terminal connected to said firstsupply potential and having a tap,

a second supply potential, and

.a diode bypass circuit comprising a second voltage divider having afirst terminal connected to the reference potential and having a secondterminal connected to said second supply potential and having a tap, and

a third diode having a first electrode connected to said tap of saidfirst voltage divider and having a second electrode connected to saidtap of said second voltage divider,

said third diode conducting to bypass a pontionof the output of saidrectifier when the rectifier output causes said third diode to conduct.

2. In a color display including a multi-beam kinesc-ope and means forproviding deflection signals for deflecting 60 the beams, a convergencecircuit for developing a signal for controlling convergence of a beam,said convergence circuit comprising a difference amplifier responsive toa deflection signal for generating a first out-put in phase with thedeflection signal and a second output 180 degrees outof-phase wtih thedeflection signal,

a potentiometer having a first terminal connected to a referencepotential and having a second terminal,

a first diode having a first electrode connected to said second terminalof said potentiometer and having a second electrode connected to theinput to said difference amplifier,

said first diode conducting to bypass a portion of the deflection signalwhen the deflection signal has predetermined values,

asszaao a full-wave rectifier responsive to the outputs of saiddifference amplifier for passing said in-phase signal when it passes inone direction a prescribed value and passing said out-of-phas'e signalwhen it passes in the opposite direction said prescribed value,

first and second supply potentials,

a first voltage divider having a first terminal connected to the outputof said rectifier and having a second terminal connected to said firstsupply potential and having a tap,

a second voltage divider having a first terminal connected to thereference potential and having a second terminal connected to saidsecond supply potential and having a tap, and

a second diode having a first electrode connected to said tap of saidfirst voltage divider and having a second electrode connected to saidtap of said second voltage divider,

said second diode conducting to bypass a portion of the output of saidrectifier when the rectifier output causes said second diode to conduct.

3. In a color display including a multi-beam kinescope and means forproviding deflection signals for deflecting the beams, a convergencecircuit for developing a signal for controlling convergence of a beam,said convergence circuit comprising a diflerence amplifier responsive toa deflection signal for producing a first output in phase with thedeflection signal and a second output 180' degrees out-ofphase with thedeflection signal,

a potentiometer having a first terminal connected to a referencepotential and having a second terminal,

a first diode having a first electrode connected to the second terminalof said potentiometer and having a second electrode connected to theinput to said difference amplifier,

said first diode conducting to bypass a portion of the deflection signalwhen the deflection signal has predetermined values,

a full-Wave rectifier responsive to the outputs of said difi'erenceamplifier for passing said in-phase signal when it passes a prescribedvalue in one direction and passing said out-of-phase signal when itpasses the prescribed value in the opposite direction,

a second diode having first and second electrodes,

means for connecting the first electrode of said second diode to theoutput of said rectifier, and

bias means connected to the second electrode of said second diode,

said second diode conducting to bypass a portion of the output of saidrectifier When the rectifier output causes said second diode to conduct.

4. In a color display including a multi-beam kinescope and means forproviding deflection signals for deflecting the beams, a convergencecircuit for developing a signal for controlling convergence of a beam,said convergence circuit comprising a diflerence amplifier having aninput responsive to a deflection signal for producing a first output inphase with the deflection signal and a second output 180 degreesout-of-phase with the deflection signal,

rectifier means responsive to the outputs of said difference amplifierfor reproducing the deflection signal with selected portions thereofinverted,

a second diode having first and second electrodes,

means for connecting the first electrode of said second diode to theoutput of said rectifier means, and bias means connected to the secondelectrode of said second diode,

said second diode conducting to bypass a portion of the output of saidrectifier means when the rectifier output causes said second diode toconduct.

5. In a color display including a multi-beam kinescope and meansproviding deflection signals for deflecting the beams, a convergencecircuit for developing a signal for controlling convergence of a beam,said convergence circuit comprising first means for attenuating adeflection signal when the deflection signal has predetermined values,

means for inverting the output of said first attenuating means when thevalue of the attenuated signal passes in one direction a predeterminedthreshold value, and for providing the attenuated signal at an outputwhen its value passes in the opposite direction the predeterminedthreshold value, and

second means for attenuating selected portions of the output of saidinverting means. 6, In a color display including a multi-beam kinescopeand means providing deflection signals for deflecting the beams, aconvergence circuit for developing a signal for controlling convergenceof a beam, said convergence circuit comprising means for inverting adeflection signal when the de flection signal has predetermined values,and

means connected to the input of said inverting means for selectivelybypassing a portion of the deflection signal.

7. In a color display including a multi-beam kinescope and meansproviding deflection signals for deflecting the beams, a convergencecircuit for developing a signal for controlling convergence of a beam,said convergence circuit comprising means for inverting a deflectionsignal when the deflection signal has predetermined values, and

means responsive to the output of said inverting means for selectivelyvarying the slope of a portion of the output thereof.

8. The convergence circuit according to claim 7 Wherein said last namedmeans comprises means for selectively bypassing a portion of the outputof said invelter means.

References Cited UNITED STATES PATENTS 12/1963 Schopp.

7/1964 Chandler.

5. IN A COLOR DISPLAY INCLUDING A MULTI-BEAM KINESCOPE AND MEANSPROVIDING DEFLECTION SIGNALS FOR DEFLECTING THE BEAMS, A CONVERGENCECIRCUIT FOR DEVELOPING A SIGNAL FOR CONTROLLING CONVERGENCE OF A BEAM,SAID CONVERGENCE CIRCUIT COMPRISING FIRST MEANS FOR ATTENUATING ADEFLECTION SIGNAL WHEN THE DEFLECTION SIGNAL HAS PREDETERMINED VALUES,MEANS FOR INVERTING THE OUTPUT OF SDAID FIRST ATTENUATING MEANS WHEN THEVALUE OF THE ATTENUATED SIGNAL PASSES IN ONE DIRECTION A PREDETERMINEDTHRESHOLD VALUE, AND FOR PROVIDING THE ATTENUATED SIGNAL AT AN OUTPUTWHEN ITS VALUE PASSES IN THE OPPOSITE DIRECTION THE PREDETERMINEDTHRESHOLD VALUE, AND SECOND MEANS FOR ATTENUATING SELECTED PORTIONS OFTHE OUTPUT OF SAID INVERTING MEANS.